Question:
Study the following and pick up the correct statements.
I. Klinefelter's syndrome is an example for trisomy in allosomes.
II. Turner's syndrome is due to monosomy in allosomes.
III. Down's syndrome is due to trisomy of $21^{\text{st}}$ chromosome.
IV. Aneuploidy is due to non-disjunction during gametogenesis.
Study the following and pick up the correct statements.
I. Klinefelter's syndrome is an example for trisomy in allosomes.
II. Turner's syndrome is due to monosomy in allosomes.
III. Down's syndrome is due to trisomy of $21^{\text{st}}$ chromosome.
IV. Aneuploidy is due to non-disjunction during gametogenesis.
I. Klinefelter's syndrome is an example for trisomy in allosomes.
II. Turner's syndrome is due to monosomy in allosomes.
III. Down's syndrome is due to trisomy of $21^{\text{st}}$ chromosome.
IV. Aneuploidy is due to non-disjunction during gametogenesis.
Show Hint
Remember the chromosomal numbers of key genetic disorders:
Down's syndrome = Autosomal trisomy (chromosome 21).
Klinefelter's syndrome = Allosomal trisomy (XXY).
Turner's syndrome = Allosomal monosomy (XO).
All of these arise due to meiotic non-disjunction of chromosomes.
Down's syndrome = Autosomal trisomy (chromosome 21).
Klinefelter's syndrome = Allosomal trisomy (XXY).
Turner's syndrome = Allosomal monosomy (XO).
All of these arise due to meiotic non-disjunction of chromosomes.
Updated On: Jul 22, 2026
- I only
- I and II only
- I, II and III only
- I, II, III and IV
Show Solution
Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Question:
The question presents four statements regarding human chromosomal disorders and aneuploidy, asking us to identify the correct ones.
Step 2: Key Concept and Approach:
We will examine each genetic disorder and its cytogenetic basis to verify the statements:
- Klinefelter's syndrome is a sex-chromosome (allosome) trisomy.
- Turner's syndrome is a sex-chromosome monosomy.
- Down's syndrome is an autosomal trisomy involving chromosome 21.
- Aneuploidy refers to an abnormal chromosome count arising from chromosome segregation errors.
Step 3: Detailed Explanation:
• Statement I (Klinefelter's syndrome): This disorder is characterized by an extra X chromosome in males, yielding a karyotype of 47, XXY.
Since it is an addition to the sex chromosomes, it is a trisomy of the allosomes.
Therefore, this statement is correct.
• Statement II (Turner's syndrome): This condition results from the absence of one of the X chromosomes in females, leading to a karyotype of 45, XO.
As it involves a missing sex chromosome, it is an allosomal monosomy.
Therefore, this statement is correct.
• Statement III (Down's syndrome): Down's syndrome is caused by the presence of an extra copy of chromosome 21, resulting in a karyotype of 47, XX/XY +21.
Since chromosome 21 is an autosome, it is an autosomal trisomy.
Therefore, this statement is correct.
• Statement IV (Aneuploidy): Aneuploidy is the loss or gain of individual chromosomes.
It is caused by the failure of homologous chromosomes or sister chromatids to segregate properly (non-disjunction) during meiotic division in gamete formation.
Therefore, this statement is correct.
Step 4: Final Answer:
Since statements I, II, III, and IV are all biologically correct, the correct option is (D).
The question presents four statements regarding human chromosomal disorders and aneuploidy, asking us to identify the correct ones.
Step 2: Key Concept and Approach:
We will examine each genetic disorder and its cytogenetic basis to verify the statements:
- Klinefelter's syndrome is a sex-chromosome (allosome) trisomy.
- Turner's syndrome is a sex-chromosome monosomy.
- Down's syndrome is an autosomal trisomy involving chromosome 21.
- Aneuploidy refers to an abnormal chromosome count arising from chromosome segregation errors.
Step 3: Detailed Explanation:
• Statement I (Klinefelter's syndrome): This disorder is characterized by an extra X chromosome in males, yielding a karyotype of 47, XXY.
Since it is an addition to the sex chromosomes, it is a trisomy of the allosomes.
Therefore, this statement is correct.
• Statement II (Turner's syndrome): This condition results from the absence of one of the X chromosomes in females, leading to a karyotype of 45, XO.
As it involves a missing sex chromosome, it is an allosomal monosomy.
Therefore, this statement is correct.
• Statement III (Down's syndrome): Down's syndrome is caused by the presence of an extra copy of chromosome 21, resulting in a karyotype of 47, XX/XY +21.
Since chromosome 21 is an autosome, it is an autosomal trisomy.
Therefore, this statement is correct.
• Statement IV (Aneuploidy): Aneuploidy is the loss or gain of individual chromosomes.
It is caused by the failure of homologous chromosomes or sister chromatids to segregate properly (non-disjunction) during meiotic division in gamete formation.
Therefore, this statement is correct.
Step 4: Final Answer:
Since statements I, II, III, and IV are all biologically correct, the correct option is (D).
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